The invention relates to the use of power amplifiers, and particularly relates to using transformers to couple a power amplifier to a load.
Employing transformers to couple a power amplifier to a load generally permits any desired voltage transformation to be achieved within an operating range. Amplifiers with relatively small supply voltages may provide large voltage swings across the load. Moreover, transformers may act as impedance matching networks in certain applications to achieve maximum power transfer to the load.
As shown in FIG. 1, a conventional power amplifier system employing a transformer to couple a power amplifier 10 to a load 12 involves a transformer 14 having a primary winding 16 and a secondary winding 18 that provides a turns ratio of N:1 as indicated. Generally, the choice of N depends on the voltage and current requirements of the load, as well as the voltage and current ratings of the amplifier 10.
Although it is desirable to provide wide swings of output current for certain applications, a large turns ratio as well as large voltage swings are generally needed to provide the large output current. Further, systems that employ a large turns ratio to provide the high current (and power) output generally result in the generation of substantial heat that must be dissipated as evenly as possible, particularly if the system or circuit includes thermally sensitive components.
There is a need therefore, for an amplifier system that provides large current swings. There is a further need for such an amplifier system that reduces localized heating.
The invention provides a power amplifier system including a plurality of amplifiers, a plurality of primary transformer windings, a single secondary transformer winding. Each of the plurality of amplifiers includes a differential input that is commonly coupled to a system input port, and each the plurality of amplifiers also includes a differential output. Each of the plurality of primary transformer windings is coupled to the differential output of one of the plurality of amplifiers. The single secondary transformer winding is inductively coupled to all of the primary transformer windings and provides a system output port to which a load may be coupled.